The present invention relates to Heating, Ventilating, and Air Conditioning (HVAC) systems and in particular to outdoor air introduced into buildings during HVAC operation through economizer dampers or non-economizer dampers.
Buildings are required to provide a minimum flow of outdoor air into their HVAC systems per the American Society of Heating Refrigeration and Air-Conditioning Engineers (ASHRAE) Standard 61.1 (ANSI/ASHRAE 62.1-2010. Standard Ventilation for Acceptable Indoor Air Quality) and the California Energy Commission (CEC) Building Energy Efficiency Standards for Residential and Nonresidential Buildings (CEC-400-2012-004-CMF-REV2). When the outdoor airflow exceeds the minimum required airflow, the additional airflow may introduce unnecessary hot outdoor air when the HVAC system is cooling the building, or introduce unnecessary cold outdoor air when the HVAC system is heating the building. This unnecessary or unintended outdoor airflow reduces space cooling and heating capacity and efficiency and increases cooling and heating energy consumption and the energy costs required to provide space cooling and heating to building occupants. Known methods for measuring the amount of outdoor airflow introduced into buildings to meet minimum requirements are inaccurate and better methods are required to improve thermal comfort of occupants, reduce cooling and heating energy usage, and improve cooling and heating energy efficiency.
U.S. Pat. No. 6,415,617 (Seem 2002) discloses a method for controlling an air-side economizer of an HVAC system using a model of the airflow through the system to estimate building cooling loads when minimum and maximum amounts of outdoor air are introduced into the building and uses the model and a one-dimensional optimization routine to determine the fraction of outdoor air that minimizes the load on the HVAC system. The '617 patent does not provide apparatus or methods to measure the Outdoor Air Fraction (OAF) defined as the ratio of outdoor airflow through the economizer or non-economizer dampers to total system airflow. Nor does the '617 patent provide methods to adjust the economizer outdoor air damper minimum damper position until OAF is within the allowable minimum regulatory requirement.
US Patent Application Publication No. 2015/0,309,120 (Bujak 2015) discloses a method to evaluate economizer damper fault detection for an HVAC system including moving dampers from a baseline position to a first damper position and measuring the fan motor output at both positions to determine successful movement of the baseline to first damper position. The '120 publication does not teach how to measure the OAF or electronically control the actuator to adjust the economizer outdoor air damper minimum damper position until OAF is within the allowable minimum regulatory requirement.
U.S. Pat. No. 7,444,251 (Nikovski 2008) discloses a system and method to detect and diagnose faults in HVAC equipment using internal state variables under external driving conditions using a locally weighted regression model and differences between measured and predicted state variables to determine a condition of the HVAC equipment. The '251 patent does not provide apparatus or methods to measure the OAF. The '251 patent does not provide apparatus or methods to measure the OAF. Nor does the '251 patent provide methods to adjust the economizer outdoor air damper minimum damper position until OAF is within the allowable minimum regulatory requirement or measure the temperature difference across the evaporator or heat exchanger to determine whether or not the sensible cooling or heating capacities are within tolerances.
U.S. Pat. No. 6,223,544 (Seem 2001) discloses an integrated control and fault detection system using a finite-state machine controller for an air handling system. The '544 method employs data regarding system performance in the current state and upon a transition occurring, determines whether a fault exists by comparing actual performance to a mathematical model of the system under non-steady-state operation. The '544 patent declares a fault condition in response to detecting an abrupt change in the residual which is a function of at least two temperature measurements including: outdoor-air, supply-air, return-air, and mixed-air temperatures. The '544 patent measures the mixed-air temperature with a single-sensor and without a minimum temperature difference between outdoor and return air temperatures. The '544 patent does not provide apparatus or accurate methods to measure the OAF. Nor does the '544 patent provide methods to adjust the economizer outdoor air damper minimum damper position until the OAF is within the allowable minimum regulatory requirement or measure the temperature difference across the evaporator or heat exchanger to determine whether or not the sensible cooling or heating capacities are within tolerances.
Carrier. 1995. HVAC Servicing Procedures. SK29-01A, 020-040 (Carrier 1995). The Carrier 1995, page 149-150, describes the “Proper Airflow Method” (pp. 7-8 of PDF) based on measuring temperature split and hereinafter referred to as the Temperature Split (TS) method. The TS method focuses entirely on measuring temperature split to determine if there is proper airflow and does not mention that temperature split can be used to detect low cooling capacity or other faults. The TS method is recommended after the superheat (non-TXV) or subcooling (TXV) refrigerant charge diagnostic methods are performed (pp. 145-149). The TS method was first required in the 2000 CEC Title 24 standards, only to check for proper airflow not for proper cooling capacity.
California Energy Commission (CEC). 2008. 2008 Residential Appendices for the Building Energy Efficiency Standards for Residential and Nonresidential Buildings. CEC-400-2008-004-CMF, California Energy Commission, Sacramento, Calif.: pp. RA3-9 to RA3-24 (CEC 2008). The CEC 2008 report provides a Refrigerant Charge Airflow (RCA) protocol disclosed in the Carrier 1995 HVAC Servicing Procedures document and defined in Appendix RA3 of the CEC 2008 Building Energy Efficiency Standards, which is a California building energy code. The Temperature Split (TS) method is used to check for minimum airflow across the evaporator coil in cooling mode per pp. RA3-15, Section RA3.2.2.7 Minimum Airflow.                “The temperature split test method is designed to provide an efficient check to see if airflow is above the required minimum for a valid refrigerant charge test.”In 2013, the CEC adopted the 2013 Building Energy Efficiency Standards and no longer allowed the TS method to check for minimum airflow due to the perceived inaccuracy of the TS method as disclosed in the Yuill 2012 report.        
Yuill, David P. and Braun, James E., 2012. “Evaluating Fault Detection and Diagnostics Protocols Applied to Air-Cooled Vapor Compression Air-Conditioners.” International Refrigeration and Air Conditioning Conference. Paper 1307. http://docs.lib.purdue.edu/iracc/1307. (Yuill 2012). The Yuill 2012 report evaluated the Refrigerant Charge Airflow (RCA) protocol including the TS method specified in the Appendix RA3 of the CEC 2008 Building Energy Efficiency Standards, which is the California building energy code. Yuill applied the TS method to cooling mode air-conditioners to determine whether an Evaporator Airflow fault (EA) is present, and if none is present to determine whether a refrigerant charge fault is present (UC or OC). Yuill 2012 evaluated the accuracy of correctly diagnosing Evaporator Airflow (EA) faults from −90% to −10% of proper airflow (equivalent to 10% to 90% of proper airflow.) Page 7 of the Yuill 2012 report makes the following statement:                “The results, overall, seem quite poor. About half of the times it's applied, the RCA protocol gives a correct result. The most serious problems are the high rates of False Alarm and Misdiagnosis (30% and 33%), because each of these outputs will result in costly and unnecessary service when the protocol is deployed. In practice, users of FDD on unitary equipment commonly have no tolerance for False Alarms, but are quite tolerant of Missed Detections, so it could be concluded that this protocol is overly sensitive.”Yuill reported that the TS method was 100% accurate for diagnosing low airflow from −90% to −50% (i.e., 10% to 50% of proper airflow), but the accuracy was unacceptable for diagnosing low airflow from −40% to −10% (i.e., 60% to 90% of proper airflow). The Yuill 2012 report identified:        “a great need for a standardized method of evaluation, because it is likely that better-performing methods currently exist, or could be developed, and could take the place of RCA, but with no method of evaluating them it is impossible to know what those methods are.”Based on the Yuill 2012, the CEC, HVAC industry experts, and persons having ordinary skill in the art no longer recommended using the TS method for checking “proper airflow” or any other fault. In 2013, the CEC Title 24 standards mentioned the TS method, but did not allow this method to be used for field verification of proper airflow. Nor did the CEC recommend using the TS method to check low capacity or other faults. Instead the CEC required other methods for field verification of proper airflow. From 2000 through 2017, the CEC has not recommended or required using the TS method to diagnose low capacity faults caused by low refrigerant charge, dirty air filters, blocked evaporator/condenser coils, low refrigerant charge, iced evaporator, faulty expansion device, restrictions, non-condensables, duct leakage, excess outdoor airflow or low thermostat setpoint, then longer compressor operation will result which wastes energy.        
California Energy Commission. 2012. Reference Appendices The Building Energy Efficiency Standards for Residential and Nonresidential Buildings. CEC-400-2012-005-CMF-REV3. (CEC 2012). CEC 2012 reference appendices of the building standards page RA3-27-28 require the following methods to measure airflow: 1) supply plenum pressure measurements are used for plenum pressure matching (fan flow meter), 2) flow grid measurements (pitot tube array “TrueFlow”), 3) powered-flow capture hood, or 4) traditional flow capture hood (balometer) methods to verify proper airflow. CEC 2012 required supply plenum pressure measurements to be taken at the supply plenum measurement access locations shown in Figure RA3.3-1. These holes were previously used to measure Temperature Split (TS), but TS is not required since the CEC and persons having ordinary skill in the art do not believe the TS method provides useful information.
R. Mowris, E. Jones, R. Eshom, K. Carlson, J. Hill, P. Jacobs, J. Stoops. 2016. Laboratory Test Results of Commercial Packaged HVAC Maintenance Faults. Prepared for the California Public Utilities Commission. Prepared by Robert Mowris & Associates, Inc. (RMA 2016). The RMA 2016 laboratory study states that the TS method was accurate 90% of the time when diagnosing low airflow (cfm) and low cooling capacity (Btu/hr) faults including excess outdoor air ventilation, blocked air filters or coils, restrictions, non-condensables, low refrigerant charge, or other cooling system faults. Page iii of the RMA 2016 abstract makes the following statement.                “The CEC temperature split protocol average accuracy was 90+/−2% based on 736 tests of faults causing low airflow or low capacity.”The prior art does not disclose a method or a need to use the TS method to diagnose a low capacity fault based on excess outdoor air ventilation, blocked air filters or coils, low refrigerant charge, restrictions, non-condensables, or other cooling system faults. Due to the poor performance of the TS method for checking low airflow from −10 to −40% as disclosed by Yuill 2012, starting in 2013, the CEC no longer requires using the TS method to check minimum airflow. Instead the CEC requires direct measurement of airflow using one of the following methods: 1) supply plenum pressure (fan flow meter), 2) flow grid measurements (pitot tube array “TrueFlow”), 3) powered-flow capture hood, or 4) traditional flow capture hood (balometer).        
U.S. Pat. No. 7,500,368 filed in 2004 and issued in 2009 to Robert Mowris (Mowris '368) discloses a method for correcting refrigerant charge (col 13:1-16).                “if the delta temperature split is less than minus the delta temperature split threshold, and the air conditioning system is not a Thermostatic Expansion Valve (TXV) system: computing one of the a refrigerant undercharge and a refrigerant overcharge based on a superheat temperature; if the delta temperature split is less than minus the delta temperature split threshold, and the air conditioning system is the TXV system: computing one of the refrigerant undercharge and the refrigerant overcharge based on subcooling temperature; and adjusting the amount of refrigerant in the air conditioning system based on one of the refrigerant undercharge and the refrigerant overcharge.”The Mowris '368 patent thus discloses a method to compute a refrigerant undercharge or overcharge based on superheat (non-TXV) or subcooling (TXV).        
U.S. Pat. No. 8,066,558 (Thomle '558) discloses a method for demand control ventilation to address the issue of temperature sensor failure using an occupancy indicator such that if a temperature sensor measurement is determined to be incorrect, unexpected or otherwise erroneous, the ventilation system can provide an amount of fresh air sufficient for adequate ventilation without over-ventilating a building.
U.S. Pat. No. 8,195,335 (Kreft '335) discloses a method for controlling an economizer of an HVAC system with an outside air stream, a return air stream, and a mixed air stream to provide outdoor air cooling to an HVAC system. The economizer includes one or more controllable outdoor air dampers for controlling a mixing ratio of incoming outside air to return air in the mixed air stream. The control method includes positioning the one or more controllable dampers in first and second configurations such that the mixed air stream has first and second mixing ratios of incoming outside air to return air in the mixed air stream. The method also includes recording first and second measures related to the temperature of the mixed air stream when the dampers are in each of the first and second configurations and based on the recorded first and second measures related to the temperature of the mixed air stream and possibly other recorded measures related to mixed air stream parameters, the method determines whether and/or how much of the incoming outside air to admit into the economizer via the one or more controllable outdoor air dampers.
U.S. Patent Application Publication No. 2014/0207288 (Belim o '288) discloses a control unit for an HVAC system comprising an economizer configured to introduce outdoor air into the HVAC system for cooling and/or ventilation purposes where the economizer is controlled by a control unit comprising a base module with: a control circuit, an interface, and first I/O means for connecting at least one sensor of the HVAC system to control circuit for delivering at least one control signal from the control circuit to control the operation of the economizer where the base module is configured to optionally receive at least one extension module, which can be snapped on and electrically connected to the base module for expanding the functionality of the control unit.
U.S. Pat. No. 5,998,995 A (Oslander '995). Oslander '995 describes a Micro-Electro-Mechanical System (MEMS) magnetostrictive magnetometer that uses, as an active element, a commercial (001) silicon microcantilever coated with an amorphous thin film of the giant magnetostrictive alloy Terfenol-D and a compact optical beam deflection transduction scheme. A set of Helmholtz coils is used to create an AC magnetic excitation field for driving the mechanical resonance of the coated microcantilever. When the coated microcantilever is placed in a DC magnetic field, the DC field will change the amplitude at the mechanical resonance of the coated microcantilever thereby causing a deflection that can be measured. The magnetometer has been demonstrated with a sensitivity near 1 μT.
U.S. Pat. No. 7,046,002 (Edelstein '002). Edelstein '002 describes a Micro-Electro-Mechanical System (MEMS) device comprising a base structure; a magnetic sensor attached to the base structure and operable for sensing a magnetic field and allowing for a continuous variation of an amplification of the magnetic field at a position at the magnetic sensor; and for receiving a DC voltage and an AC modulation voltage in the MEMS sensor or device; a pair of flux concentrators attached to the magnetic sensor; and a pair of electrostatic comb drives, each coupled to a respective flux concentrator such that when the pair of electrostatic comb drives are excited by a modulating electrical signal, each flux concentrator oscillates linearly at a prescribed frequency; and a pair of bias members (mechanical spring connectors) connecting the flux concentrators to one another.
U.S. Pat. No. 6,215,318 (Schoefthaler '318). Schoefthaler '318 describes a MEMS magnetic field sensor including a printed circuit trace device, which is suspended above a substrate and is capable of being deflected elastically. Also included are a first capacitor plate device that is joined to the printed circuit trace device and is able to be deflected together with the printed circuit trace device, and a second, fixed capacitor plate device that is joined to the substrate and forms a capacitor device by interacting with the first capacitor plate device. A magnetic field sensing device conducts a predetermined current through the printed circuit trace device and measures the change in capacitance of the capacitor device arising in dependence on an applied magnetic field. The magnetic field sensing device can also be designed in such a way that it can be calibrated by calibration current loops.
U.S. Pat. No. 7,895,892 (Aigner '892). Aigner '892 describes a Micro-Electro-Mechanical Systems (MEMS) rotation sensor with a substrate and a first surface and a second surface. A shear-wave transparent mirror is arranged on the first surface of the substrate, and a shear-wave isolator is arranged above the shear-wave transparent mirror, the shear-wave transparent mirror and the shear-wave isolator being arranged separated from each other to define a Coriolis zone there between. A bulk-acoustic-wave resonator is arranged above the shear-wave isolator, and a shear-wave detector is arranged on the substrate in a direction, in which a shear-wave generated by the bulk-acoustic-wave resonator upon rotation propagates.
U.S. Pat. No. 6,131,457 (Sato '457). Sato '457 describes a MEMS three-dimensional acceleration sensor having a magnetic body including a mass point, mounted to a vibrator having three-dimensional freedom and an axis in line with a Z-axis within the orthogonal spatial coordinate axes of X, Y and Z. The acceleration sensor includes four or more detector elements including at least two positioned along the X-axis and at least two positioned along the Y-axis with their centers located along a concentric circle around the origin point of the coordinate axes. The sensor detects acceleration in a direction of the X-axis through a relative difference in output voltage between two of the detector elements positioned along the X-axis due to a variation of magnetic field intensity from the magnetic body, acceleration in a direction of the Y-axis through a relative difference in output voltage between two of the detector elements positioned along the Y-axis, and acceleration in a direction of the Z-axis through an aggregate sum of the output voltages of all the detector elements. The acceleration sensor thus has a wide dynamic range as well as high detection accuracy, and may be produced having a reduced size.
U.S. Pat. No. 7,131,998 (Pasolini '998). Pasolini '998 describes a device for measuring the relative angular position of two bodies with respect to a point is provided with a first measuring element and a second measuring element, relatively movable with respect to one another and connectable to a first body and a second body, respectively; the first measuring element includes a first inclination sensor, which has a first detection axis and supplies a first inclination signal, correlated to a first angle of inclination of the first detection axis with respect to a reference axis, and the second measuring element includes a second inclination sensor, which has a second detection axis and supplies a second inclination signal, correlated to a second angle of inclination of the second detection axis with respect to the reference axis.
U.S. Patent Application Publication No. US20050253710 (Eskildsen '710). Eskildsen '710 describes a MEMS-based overhead garage door intrusion sensor for a security system, such as a residential/home security system, for detecting an intrusion through an overhead garage door. In one embodiment, a MEMS sensor accelerometer is mounted with a sensitive axis of the MEMS device, along which the MEMS device measures acceleration/gravity, pointing vertically downward towards the earth when the overhead garage door is closed, such that the MEMS sensor measures a 1 g acceleration/gravity force, and when the overhead garage door is open, the sensitive axis of the MEMS device points horizontally with respect to the earth, such that the MEMS sensor measures a 0 g acceleration/gravity force, such that the output of the MEMS sensor, indicating either a 1 g or a 0 g measured acceleration/gravity force, indicates whether the overhead garage door is respectively closed or open. Alternatively, the MEMS sensor can be a MEMS switch. An ASIC or microcontroller can monitor the output of the MEMS sensor, and one embodiment employs wireless RF technology.
California Energy Commission. 2016. Reference Appendices the Building Energy Efficiency Standards for Residential and Nonresidential Buildings. JUNE 2015 CEC-400-2015-038-CMF. (CEC 2016). The CEC 2016 Reference Appendices of the Building Standards JA6.3 Economizer Fault Detection and Diagnostics (pp. JA6-7 through JA6-12), requires economizer controllers to be capable of detecting the following faults: 1) air temperature sensor failure/fault, 2) not economizing when it should, 3) economizing when it should not, 4) damper not modulating and 5) excess outdoor air. However, the CEC 2016 does not describe methods to diagnose or evaluate these faults. Therefore, an unresolved need remains to develop apparatus and methods for evaluating economizer faults to improve HVAC energy efficiency.